1. Field of the Invention: This invention relates to mining machinery for underground mining operations and more particularly, to drum cutter mining machines having a drive gear wheel meshing with uniformly spaced horizontal teeth extending between two spaced apart cheek plates forming a gear rack, a plurality of which extends along the course of travel of the mining machine with adjacent racks having shoulders engaged in a cavity of a mounting bracket while a bracket wall section engages in a cavity formed in an underside of a tooth of the gear rack.
2. Description of the Prior Art: A gear rack made up of individual rack segments for advancing movement of a drum cutter mining machines along a mine face are well known in the art. West German Patent Application No. P 36 24 109.1 discloses such a gear rack of which the individual rack segments have shoulders below the rack teeth to engage in the cavity of a mounting bracket. Connecting bolts extending at right angles to the elongated length of the gear rack secure adjacent rack segments to one bracket. The bracket is in turn secured to a longwall face conveyor situated below the gear rack to support the rack.
The purpose of such an arrangement for supporting a gear rack is to better absorb the tilting forces caused by the drum cutting machine when it is moving along the gear rack. Such forces are induced by unilateral mounting of rack segments which is intended to prevent deformations of the bracket wall. For reasons of manufacture, but even more so for reasons of assembly, the shoulders of the rack segments each extend a distance approximately corresponding to the pitch of the rack teeth. The shoulder engages in the cavity of the mounting bracket in a way to allow lateral movement of the shoulder in the cavity of the bracket. Consequently, the gear rack segments adjacent to each other can move horizontally and abut against each other because of such limited lateral movement. When the drive gear of the drum cutter-loader passes from one rack segment to the adjacent rack segment, the transition is made more difficult because the tooth width of the drive gear is large due to the tooth load caused by the high feed force needed to move the mining machine. The width of the gear teeth present operational difficulties as the gear teeth pass between the two cheek sections at opposite sides of the rack segment. A gap between sides of the gear teeth and the cheek sections of the rack segment is, however, necessary in order to accommodate lateral misalignment between rack segments when the longwall conveyor is advanced toward the mine face. Collisions between the rack segments and drive gear at the crossing points between rack segments due occur from time-to-time under these circumstances. Such collisions impair the travelling motion of the cutter-loader, but, above all, they increase wear, not only in the area of the drive gear teeth but also on the rack segments themselves.
For this reason, it has already been disclosed in West German Patent Application No. P 36 23 387, that the rack segments be equipped on the side turned away from the longwall conveyor with a ledge-like foot which produces either a rigid or a limited longitudinally movable communication between the rack segment and side bracket on the conveyor. At the front, the foot and the rack segments have shoulders or cavities corresponding to each other and engage with each other at the joint. Thus, vertical or horizontal movements of the rack segments relative to each other is prevented, but the longitudinal movement of the rack segments against each other is still possible.